Studies of issues related to device to device (D2D) have begun by 3GPP RAN in an LTE system, which are intended to evaluate services between geographically neighboring devices in the LTE. D2D-related operations may include D2D discovery and D2D communications.
In the D2D discovery, a user equipment (UE) selects a resource from a configured resource pool to transmit a discovery signal. The discovery signal at least contains a discovery message, and may possibly contain discovery preamble information. According to current progress, it is proposed to repeatedly transmit a discovery message many times in a discovery period, so as to improve D2D discovery performance.
For example, in a discovery period, a discovery message carrying a discovery medium access control (MAC) protocol data unit (PDU) may be transmitted in a manner of repeated transmission, so as to improve a D2D discovery probability.
And on the other hand, another important subject of the D2D is the D2D communications. According to current discussion progress, when a D2D transmitter end UE transmits D2D broadcast data, the method of multiple times of retransmission is also used to improve channel quality.
It should be noted that the above description of the background is merely provided for clear and complete explanation of the present disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the present disclosure.